<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    let a = '';
    let b = null;
    if (a === b) {
        console.log('a === b');
    } else if (a < b) {
        console.log('a < b');
    } else if (a > b) {
        console.log('a > b');
    } else {
        console.log('没有这种情况')
    }
</script>
</body>
</html>